Tesco's decision to sell chickens for £1.99 in its stores is a telling indictment of our attitude to food. It's no longer about nutrition or health, it's simply a matter of marketing.

While researching my book, We Want Real Food, I was frequently struck by the way agrarian societies - however poor - would produce food in the best way they knew how, without compromise. Typical were the people of Loetschental, a remote valley high in the Swiss Alps. When the American dentist-turned-nutritionist Weston Price visited the valley in the 1920s he found a supremely healthy community with no infections, no degenerative disease and no tooth decay. He discovered there had never been a case of TB in the valley, even though "the white scourge" was rife in Swiss cities.

The people of the valley lived principally on dairy foods produced from cows grazing the herb-rich Alpine pastures. In spring, when the snow retreated and they turned their cows out on to the fast-growing pasture, they would fashion the first butter of the year into a candle. This would be the centrepiece of a thanksgiving service in the village church - such was the respect the people had for the health-giving properties of their food.

It would be inconceivable that they would attempt to produce cheaper butter by feeding some of the cows on vegetable scraps or wheat bran. Today science is revealing that milk produced from cows on fast-growing spring pastures is high in fat-soluble vitamins, omega-3s and the cancer-fighting CLA, all the things that protect people from disease. Without knowing the science, agrarian communities invariably knew the foods that would keep them healthy. These were available to all, rich and poor.

Something of that philosophy survived in my own childhood days back in the 1950s. The quality of staple foods varied, of course, but there was a general presumption that farmers would produce them in the best way they knew how. To this day I believe the local milk delivered to our Reading council estate was nutritionally superior to anything available now - including organic milk.

That culture has been totally eclipsed by the profit-centred philosophy of modern marketing. Supermarkets stock 50 different brands of instant coffee so there is something - so they claim - to suit all requirements. Tesco's £1.99 chicken sits alongside free range, organic and a host of other birds. It's called market fragmentation, or some such thing, and it allows the company to maximise its take at the checkout. It's also supposed to give consumers a greater choice.

In reality there's no choice at all. While the strategy may work for washing-up liquid or torch batteries - where the consumer can pretty well estimate what they're getting for their money - it's a nonsense when applied to food. Until science comes up with a way of measuring the total nutrient content of a food, there's no way the consumer can make a sensible choice.

It's now becoming clear that the healthiest chicken - like the healthiest dairy products - comes from birds that are raised on fresh pasture. In a society that cared about the health of its citizens, this kind of chicken would be the norm. If there were people in society who were unable to afford it, the question would become one of income distribution and social justice. It would not become a justification for producing a less-healthy version.

Tesco managers may convince themselves that in offering foods that are less than the best they are simply giving all their customers what they want. But measured by the food culture of the Loetschental it looks more like treating them with contempt.